This invention relates to a method for determining the state of a movement or a stoppage of a yarn being fed to a textile machine, and subsequently for further verifying that the yarn is correctly fed to the textile machine. The method involves determining and monitoring the state of movement or stoppage of a yarn fed to a textile machine, by using an optical sensor.
The invention also relates to a device for implementing the method for determining the state of movement or stoppage of a yarn fed to a textile machine.
Various devices and methods are already known for determining the state of progress or stoppage or, in general, the state of movement of yarn fed to a textile machine.
One of these devices has substantially a "tuning fork" configuration and basically comprises a sensitive magnetostrictive piezoelectric element or the like which converts vibrations generated by a feeler member of tuning fork configuration, in contact with the yarn, into electrical signals. The electrical signals are used to measure the yarn movement by an electrical or electronic circuit which controls the machine operation.
Such a device, or similar devices, comprising generally a feeler member in direct contact with the yarn and connected to a sensitive element of the aforesaid type, has considerable drawbacks.
In this respect, it is substantially influenced by vibration or noise external to the machine or generated within the machine during its operation.
These noises and vibrations considerably limit the application of such devices to textile machines.
This is because such noises and vibrations in many cases exceed the vibration generated by the yarn of the feeler member and transmitted to the sensitive element. Because of such noise, the sensitive element may therefore generate spurious signals which prejudice the proper operation of the machine. Consequently, such devices must necessarily be combined with anti-vibration members which limit these external influences in determining the state of the yarn.
Other devices of electrostatic type are known, but these are easily influenced by the conditions of the environment in which they operate, and by the humidity and type of yarn.
Such devices, which operate (as is well known) on the basis of the electrostatic charges generated by the moving yarn with which they cooperate, are considerably influenced by the moisture content of the yarn, to the extent that a yarn which is too moist is unable, during its passage over the corresponding device, to leave or generate electrostatic charges which are sufficient for the corresponding device to detect effective movement.
Similar problems arise when the yarn is too dry or too easily electrifiable, i.e., susceptible to being electrified such as yarns containing wool, which electrify excessively to falsify the measurement of the state of movement by the sensor device. In such a case, the sensor device is able to detect a state of movement of the yarn even if it is not moving.
Other photoelectric cell devices are also known for determining the state of progress of yarn fed to a textile machine.
Briefly, these operate on the basis of interrupting a light beam generated by a light emitter and directed onto a receiver member connected to a control circuit. When the yarn positioned between the emitter and receiver moves, it shifts in position between these members and interrupts the light beam present between them.
This enables the control circuit to sense the movement and to control, in a known manner, the operation of the textile machine or that part of it to which the yarn is fed.
Such a photoelectric cell device requires precise setting and precise positioning relative to the emitter and receiver to ensure that during each stage of operation of the textile machine the yarn always remains between the emitter and receiver.
These devices are consequently difficult to apply, an additional complication being that they have to be positioned as close as possible to the bobbins from which the yarn unwinds, because only in such a position, the yarn has sufficient agitation to give it a high probability of detection.
In addition, to enable the light beam passing between the emitter and receiver to be easily interrupted by the yarn and enable the control circuit to generate an appreciable signal indicative of the movement of the yarn, the light beam must have a cross-section equal to or only slightly greater than that of the yarn being monitored. Because of this, requirement such a device is very sensitive to the accumulation of dust or residues left on it by the moving yarn. The dust or residues can obscure the light beam, which typically has a very small cross-section (such as that of the yarn).
This obscuring adversely affects the proper operation of the device.